1. Field of the Invention
The disclosures herein generally relate to a concentrator photovoltaic cell.
2. Description of the Related Art
A concentrator solar power generation unit which includes a first optical system for concentrating a solar light, a solar battery cell, and a columnar optical member made of glass containing sodium is known. The columnar optical member is vertically arranged directly above the solar battery cell such that a bottom edge surface of the columnar optical member faces the solar battery cell. The columnar optical member guides the solar light concentrated by the first optical system to the solar battery cell. The concentrator solar power generation unit also includes a sealing resin which covers the columnar optical member and the solar battery cell which faces the bottom edge surface of the columnar optical member. The sealing resin contains at least 10 weight percent of a fluorinated silicone resin.
The solar battery cell, such as InGaP/InGaAs/Ge, has a multi-junction structure which is formed on a chip by the crystal growth of a group III-V compound semiconductor, on a single crystalline substrate such as GaAs. The multi-junction structure includes plural types of p-n junctions whose absorption wavelengths are different from each other, which may be layers including a bottom junction layer, an intermediate junction layer, and an upper junction layer, laminated sequentially (Japanese Unexamined Patent Application Publication No. 2007-201109, Sol. Energy Mater. Sol. Cells 90 (2006) p. 3068.).
The concentrator photovoltaic cell in the related art uses the solar battery cell which faces the bottom edge surface of the columnar optical member to perform a photoelectric conversion of the light concentrated by the first optical system and the columnar optical member which is a second optical system.
The solar battery cell has a multi-junction structure where a plurality of cells are connected in series and the band gap of each cell decreases from a front side to a back side in a light incident direction. This arrangement series absorb light from shorter wavelength to longer wavelength successively, from the front side to the back side in the light incident direction.
It may be noted that the short wavelength light is easier to be scattered by minute particles in the atmosphere than the long wavelength light. In particular, a period of time such as the morning and evening, in which a light path in the atmosphere is longer than that of the daytime, the short wavelength light is easier to be scattered by minute particles in the atmosphere than the long wavelength light. As a result, the performance of the multi-junctional solar battery cell is limited by a lower current amount of the short wavelength range cell in the morning and evening, resulting in overall efficiency being decreased.
The lower the visibility becomes due to an atmospheric condition, the more prominent such a phenomenon becomes. This is because the short wavelength light is scattered by minute particles floating in the atmosphere, resulting in received light quantity of the short wavelength light having a high energy being lowered.
As mentioned above, the conversion efficiency of the concentrator solar power generation unit in the related art is limited by the performance of the short wavelength cells.